No those other guys don't have to be named because they have nothing to do with the plot. Fett, on the other hand, is the guy who hunts down the Millennium Falcon, takes Han away to Jabba the Hutt, and is thus resposnible for setting up the beginning of the next movie, which starts off assuming we all know his name even though they don't so much as mention it in passing throughout the entirety of ESB. He's not just significant to fans (heck I honestly am not even a fan of the character myself), he's significant to the story of ESB. Even if you REALLY wanna have it to where we don't even know his name, we should at least have something to call him. Name one other major character in the entire saga who is simply known as "that person that does that thing"